dmaengine: mic_x100_dma: use the new helper to simplify the code

Use dmaenginem_async_device_register() to simplify the code:
    remove the mic_dma_unregister_dma_device()

Signed-off-by: Huang Shijie <sjhuang@iluvatar.ai>
Signed-off-by: Vinod Koul <vkoul@kernel.org>